The present invention relates to a method for determining the start and the end of an automatic braking process while a vehicle is being braked in order to optimize triggering of the automatic braking process.
A basic method for shortening the braking path in critical driving situations is described in DE 40 28 290 C1, in which an automatic braking process is triggered when the actuation speed of the brake pedal exceeds a threshold value. Directly after the automatic braking process is triggered, a brake pressure is built up which is greater than that which results from the position of the brake pedal. Thereafter, an emergency situation is detected and shortening of the braking path is brought about.
The earlier the triggering of the automatic braking process, the greater the shortening of the braking path achieved during the process, in particular because the vehicle braking path is mainly determined by the deceleration at the start of the braking process when the vehicle is at maximum speed. However, the emergency braking must not be triggered too early since unexpectedly violent braking outside emergency situations can startle the driver and cause him or her to experience reactions of panic and fright which are inappropriate for the situation. in addition, violent braking in traffic situations which do not require such braking may surprise the drivers of vehicles travelling behind so that they no longer react correctly and may drive into the vehicle travelling ahead.
For these reasons, when fixing the threshold value a compromise must be made between the earliest possible triggering, that is to say low threshold value, and avoiding unnecessary triggering, that is to say a high threshold value.
An object of the present invention is to optimize the triggering of the automatic braking process.
This object has been achieved according to the present invention by providing that a threshold value used as the criteria for triggering the automatic braking process is determined by multiplying a fixed threshold value by at least one factor which is a function of a driving state variable.
Furthermore, although a fixed threshold value is specified, this threshold value is matched to different driving situations by being multiplied by one or more factors. For this purpose, the at least one factor is determined as a function of a variable which represents the driving state of the vehicle. The variables which represent the driving state are to be understood here to include not only physical variables which characterize the movement of the vehicle but also control elements which can be actuated by the driver and influence the movement behavior of the vehicle. Information on the fixed threshold value and on the automatic braking process can be found in aforementioned DE 40 28 290 C1.
In accordance with one embodiment of the invention one factor is determined as a function of the speed of the vehicle and a further factor is determined as a function of the travel of the brake pedal experienced. To this end, the factors can each be stored independently in a characteristic curve. It is also possible to store the product of a plurality of such factors directly in a common characteristic curve diagram.
Further features of the present invention serve, on one hand, to prevent undesired triggering of the automatic braking process when the brake pedal is lightly touched and, on the other hand, to filter out small, rapid movements of the brake pedal which are produced even during constant braking by the driver. These movements are caused for example by the play of the brake pedal in the brake booster. In addition, the present invention contemplates criteria for terminating the automatic braking process. Switching off of the braking process must ensure termination when the driver wishes to finish braking or when the vehicle has come to a standstill.